Influence of cloudiness on sunshine duration

Abstract

This paper analyzes the influence of cloudiness and cloud genera on sunshine duration based on a very long homogeneous daily nephological and sunshine duration data series for the City of Krakow. Quadratic regression was used to describe the relationship between sunshine duration and cloudiness. It has been shown that cloudiness affects sunshine duration the most in June and July, and the least in December, January and February. High clouds (Cirrus, Cirrostratus, Cirrocumulus) do not interrupt the recording of sunshine duration even when they completely cover the sky. Layered clouds such as Stratus and Nimbostratus, on the other hand, do not transmit solar radiation at all. The degree of influence of different cloud genera on sunshine duration changes very little from season to season and with respect to the position of the Sun over the horizon. When the Sun is positioned higher over the horizon, clouds are less able to weaken solar radiation, resulting in larger sunshine duration values. This is especially true with respect to the following clouds: Cirrus, Cirrostratus and Cumulus. It has been shown that daytime sunshine duration patterns can be a very good indicator of cloud type and cloudiness variability. Copyright  2011 Royal Meteorological Society KEY WORDS cloudiness; cloud cover; cloud genera; sunshine duration; solar radiation; Krakow Received 24 May 2010; Revised 25 April 2011; Accepted 26 April 2011The relationship between sunshine duration and cloudiness is so obvious that it seems that there is no need to analyze it. Yet the mechanism of the impact of cloud cover on the duration of solar radiation is very complex and has not been fully analyzed to date. The climatologic literature usually treats the impact of cloudiness on sunshine duration in terms of the extent of cloud cover without taking into account the different possible cloud genera. Yet simple measurements and observations indicate that even when the sky is overcast with high clouds (e.g. Cirrostratus), solar radiation still reaches the surface of the Earth without impediment. On the other hand, layered low and middle clouds (e.g. Nimbostratus) impede direct radiation. In both cases, the sky is reported as overcast (8/8), which suggests a lack of recorded evidence of sunshine.The problem of the differential absorption and transmission of solar radiation energy by various genera of clouds, despite its fundamental significance in climate science, has not been adequately addressed thus far in the scientific literature. This may be because of the fact that clouds change constantly, thus it is challenging to adequately determine their physical properties. Groundbased weather stations report only visual cloud observations and measure the height of the cloud base. Within one such climatologic observation, several genera and species of clouds may be present at the same time, which * Correspondence to: Dorota Matuszko, Institute of Geography and Spatial Management, Jagiellonian University, ul. Gronostajowa 7, impedes the measurement of h...

Sunshine duration variability and trends in Italy from homogenized instrumental time series (1936–2013)

“…The comparison between TCC and SD records over Italy has been performed over the 1958–1995 period, using the data set of Maugeri et al [], with data available until 1995. This data set contains only TCC data, whereas no information is available for cloud amount by low and middle clouds, which would be a better variable for investigating the cloudiness‐SD relationship [e.g., Xia , ; Matuszko , ].…”

The signal of aerosol‐induced changes in sunshine duration records: A review of the evidence

“…[], Figure 10). Therefore, a large literature record relating these two magnitudes and studying their annual, seasonal, and monthly evolution is available [e.g., Fox , ; Angell et al ., ; Angell , ; Jones and Henderson‐Sellers , ; Weber , ; Palle and Butler , 2001; Curto et al ., ; Matuszko , ]. But this relationship is not always simple and linear and can be affected by several factors, such as changes in atmospheric transparency resulting from aerosols or changes in the properties of clouds.…”

Sunshine duration and global radiation trends in Italy (1959–2013): To what extent do they agree?

“…Causes of these variations are complex and not yet completely understood, especially if studies regarding different areas are compared. Major causes are thought to be related to changes in anthropogenic aerosols and cloud characteristics [Liepert et al, 1994;Stanhill and Cohen, 2001;Wild, 2009Wild, , 2016Chiacchio and Wild, 2010;Xia, 2010;Matuszko, 2012;Bartók, 2016]. Clouds are supposed to be the major contributors to the E g↓ variability at interannual scale, while atmospheric aerosols contribute especially at decadal scale [Wang et al, 2012;Wild, 2016] even if they are not completely independent [Ramanathan et al, 2001;Xia, 2012].…”